Deformation Characteristics of Combined Heavy Metals-Contaminated Soil Treated with nZVI through the Modified Slurry Consolidation Method

Abstract

Nanoscale zero-valent iron (nZVI) has been widely applied to remediate heavy metal-contaminated soils and water. Its in situ treatment of combined heavy metal contaminated soil, followed by backfilling or other sustainable reutilizations, attracted attention to the treated soil’s deformation characteristics. In this study, soil samples were prepared using the modified slurry consolidation method to simulate the natural settling of backfilled soil and optimize the reactivity between nZVI and contaminants in soil. The deformation characteristics of natural soil, contaminated soil, and soil treated with varying dosages of nZVI (0.2%, 0.5%, 1%, 2%, and 5%) were investigated. Moreover, the plasticity indexes and particle-size distribution of the samples were examined through Atterberg limits and laser-diffraction particle-size analysis. After a 4 d slurry consolidation process, a typical result indicated the immobilization efficiency of all three heavy metal ions achieved over 90% with 2% nZVI. The presence of three heavy metal ions decreased the Atterberg limits and increased the compression index, permeability, and consolidation coefficient of the soil. Conversely, the introduction of nZVI increased plasticity and resulted in higher permeability, stable secondary consolidation, and less swell. Microscopically, with an increase in the dosage of nZVI, the soil aggregates transformed from a weak chemical bond with insoluble precipitates/iron oxides to larger aggregates consisting of nZVI/-soil aggregates, thereby enhancing the soil skeleton. This study shows improved permeability and deformation characteristics in nZVI-treated combined heavy metal-contaminated soil, offering valuable insights for practical nanomaterials’ in-situ treatment in engineering applications.